Abstract: A drive circuit for a photoelectric sensor which automatically adjusts the sensor response time with adjustments in the drive current to the light source based on a desired sensing distance. The drive circuit includes an oscillator for establishing an output signal having an output frequency. An output of the oscillator is provided as an input to an adjustable current source. The current source is connected to the light source for providing the drive current to the light source at the output frequency. A peak detector is connected to a lead of the light source for detecting a feedback voltage proportional to the drive current through the light source. The feedback voltage is provided as an input to the oscillator, and the output frequency of the oscillator is variable depending on the feedback voltage so that variations in the drive current result in corresponding variations in the output frequency and, therefore, the frequency of the drive current.

Abstract: An overcurrent protection circuit is provided with a counter which permits a preselected number of reinitiations of current following the detection of an overcurrent condition. Each stoppage of current in response to the detection of an overcurrent condition is followed by a predetermined time delay and a subsequent reinitiation of current. After the predetermined number of reinitiations, current is permanently stopped from flowing between first and second circuit points until a manual reset occurs.

Abstract: An asynchronous photodetector circuit is provided to interrogate incoming signals and determine whether the frequency of those incoming signal pulses is acceptable. The circuitry of the present invention permits a series of incoming pulses to be interrogated to determine whether the frequency of those pulses is acceptable and can be assumed with confidence to be emanating from an appropriate light source. Upon the receipt of a first input signal pulse, a time window is created by the present invention to define a period to time during which a subsequent input signal pulse is to be expected. Other than during the duration of the time window, the present invention will not accept an input signal pulse and will not count that pulse as having been received. Each properly received pulse creates a subsequent time window until a predetermined number of consecutive pulses is received during their time windows. When that predetermined number is received, a signal is provided.

Abstract: An electronic circuit for interfacing a sensor of either current sourcing or current sinking type to a data bus requiring signals of predetermined characteristics, the circuit including first and second level comparators set to different reference levels so as to define a window between the reference levels at which neither comparator is actuated. A sensor input terminal is biased to a level between the reference levels of the comparators, but varies to a level outside the window in response to current flowing from or into the sensor terminal. The comparator output terminals are connected to an output circuit which produces a signal suitable for transmission on the data bus in response to actuation of either comparator.